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FSAE.com Forums FSAE.com Forums Open FSAE Discussion Hey guys,How do you adjust your fsae car's center of gravity?|
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I kown 2 ways now：
1. lengthen or shorten the pull/push rod 2.change the initial suppresses of the suspension spring I don't kown whether these are right or not please guys tell me more about this many tks |
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Are you sure you don't mean ride height (the distance from the ground to the lowest point of the sprung mass(i.e. undertray, chassis))?
"He who dies with the most toys wins" |
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In my opinion,the ride height and the center of gravity are almost the same. Because you can easily adjust one to modify the other one
but want i'd like to know is how to adjust either one of them? can anyone tell me?? |
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Oh, in that case, I would like to run my chassis underground please. Kthanksbye.
You should be running your car at the minimum ride height (1"). When you are adjusting your suspension, you usually don't want to preload your spring...So if you are trying to raise ride height, you don't want to keep jacking up the perches until the spring is preloaded. Spring preload takes away rebound travel. In general, you don't want to do this. Usually, the best way to adjust ride height is with the pushrod. The reason you do it this way is because your bellcrank remains in the designed position. If you move the spring perch the BC moves and you might end up at a different spot on your wheel rate curve. However, when testing, I will always adjust the spring perches, for two reasons. The adjustments are easier to make, and are easier to measure. Also, you can do the same adjustment to both wheels so you don't add any wedge to the car. Generally, after a test session, if we change the rake angle of the car a lot, I will go back and put the spring perches where they are suppose to be and change the pushrod length to compensate. Mike |
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There is a big problem to adjust the CofG (itself) of a F-SAE car: The lack of minimun weight like in F1.
Since there is no limit for your cars weight you always try to make it as light as possible and we dont use ballast on the bottom of the car to reduce your CofG. You do change your ride height according to your suspension system set-up (and the methods you said are correct) but not with the proper intention to reduce nor increase your CofG. Gian Flavio Violi B. F-SAE USB |
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I use a warp bubble set at factor 9 for maximum COG reduction.
University of Oklahoma Alum '09 Sooner Racing Team Cooling Lead '09 Engine Lead '08 sae.ou.edu "Remember, if you can't fix it with a hammer, you've got an electrical problem" |
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this is one of the methods we've used in the past
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I have seen teams with bell cranks that have two attachment points for the push/pull rods on their bell cranks so that they can quickly and dramatically adjust the ride height (ie CoG) of their car for the acceleration event. The placement of the attachment could affect your motion ratio though but for acceleration I don’t know how much that really matters.
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Jamie, the motion ratio change is actually the primary reason for using that kind of bellcrank. Making the car softer in ride will help with traction more than a small increase in CG (for a typical FSAE car). "Gute Fahrer haben die Fliegenreste auf den Seitenscheiben." --Walter Röhrl |
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If you really mean adjustment of the CoG: Just use a simple undertray made of 20mm thick deuterated uranium sheet alloy with a density of 25 like F1 did some years ago
 Works fine if you only care about the CoG though  DART Racing e.V., Darmstadt Alumni Technical Director Suspension & Brakes 2005-2007 Brake System Developer 2005 - 2008 CFRP Rim Specialist 2008 Test Team and Driver 2005-2009 Adding power makes you faster on the straights. Subtracting weight makes you faster everywhere. Colin Chapman |
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hi mike I have something disunderstand to your reply. when change the pushrod,how can u remain the bellcrank in the designed position? ie,if you change the length of pushrod,the force affact on the spring should change accordingly. so the spring changes, and the bellcrank changes too. is that right? or u just ignore the changes caused by this ? |
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come on man, who want to increase his own weight if he could keep a fitting body? We actually don't want to add another weight on my car! |
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can I understand like this: the motion ratio actually relates to the suspension ratio(ie. the stickness of suspension)? |
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sorry I don't actually understand the pic you posted. I can't see clearly how u change the cog. can you explain it clearly,better with pic thanks guy |
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what you've got there is 20kg of steel bar bolted to the roll hoop. It changes the CoG height, if you don't understand how then give up.
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Icyhott, Generally, when you change the pushrod length, you are doing so on the left and right side of the car (so that you jack the car up or down, without adding any cross weight (wedge)). If this is true, then changing the pushrod length doesn't change the load on the tire, which means the spring will not deflect any more or less. ---- Mike Cook It's an engineering competition, not an over-engineering competition! |
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Damn Ryan. I had no idea that was why. I feel a little silly for thinking that now.
Icy, keep looking at MalcolmG's picture. I missed it the first time i looked at it because it looked like a part of the trailer. Look at what is attached to the roll hoop. Obviously Malcolm is joking around with you. Edit:I didn't notice that Malcolm posted on this until after i posted. What is that attachement really for? Transporting the car? |
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but the angle between pushrod and bellcrank changes，which means the arm of force changes,and the load on tire is constant (I kown this),so the force of spring will have to change |
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I didn't understand the pic either. the trailer u thought is attached on the roll hoop,so the car is not suspended. I thingk Malcolm's pic is posted on the wrong place and has nothing to do with the topic. what do you think ? |
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FSAE.com Forums FSAE.com Forums Open FSAE Discussion Hey guys,How do you adjust your fsae car's center of gravity?